Voltmeter



(No Model.)

B. R. KNOWLES. VOLT METER.

4 UNITED STATESPATENT OEEIcE.

EDWARD R. KNOWLES, or MIDDLETOWN, coNNEorIoUT, Assrenoa'ro TI-lE SOHUYLER ELECTRIC COMPANY, or CONNECTICUT.

VOLTMETER.

SPECIFICATION forming part of Letters Patent No. 520,964, dated June 5,1894.

Application filed December 14, 1893. Serial No- 493.6'74=. (Ne model.)

To all whom it may concern;

Be it known that I, EDWARD B. KNOWLES,

a citizen of the United States, residing at Middletown,in the county of Middlesex and State of Conn ecticut, have invented certain new and useful Improvements in'Voltmeters, of which the following is a specification.

The object of the invention is to enable the field coils to be brought close together so as to nearly surround the needle and thus give a stronger action thereon. Thedamping device is placed outside of the coils and consists of a fan blade in a closed chamber. The strength of the permanent magnet is adjustable by means of a soft iron'bridge, and the magnet is set at an angle to the field coils in order to give the needle a longer range of movement.

In the drawings, Figure 1 is a front elevationvof the instrument. Fig. 2 shows the removable needle frame, needle and index.

Fig. 3 is a top plan view of the same with the cap removed. Fig. 4 is aperspective view of the upper part of the frame with the cap removed. Fig. 5 shows the spindle, index and fan. Fig. 6 is a cross section of the cap and Fig. 7 is a cross section of the frame.

On an insulating base A are mounted the field coils B wound on a core 0 of non magnetic material, and symmetrically arranged above and below a middle flange c on the core. In this fiangeisatransverse socket to receive snugly a removable frame D, preferably rectangular and quite thin, as shown in Fig. 2.

The inner end of the frame carries an adj ustable bearing 01 for the spindle E, the upper end of which passes through the bottom of a box D forming the outer end of the frame. A cap (1 closes the top of the box and has in it a bearing d for the outer end of the spindle. Thesespindlebearingsarepreferablyjeweled. The spindle carries the needle e of soft iron made quite thin to compel it to stand exactly in line with the lines of force. The index E is also secured to the spindle at substantially right angles to the needle and is provided with a counterweight e which tends to bring it to a vertical position. Inside the box are two radial partitions preferably quadrant sectors d placed opposite each other. The spindle is provided with a fan F composed of two oppositelydisposed blades, each lying in the space between the sectors. When the cover of the box is on, the fan makes a close fit with .the inside of the box, but does not touch it at any point. Any movement of the spindle moves the fan with it, but because the fan fits closely in the box the air confined between it and the sectors cannot readily escape, and so the sudd en movementof the spindleisdamped.

The permanent magnet Gis secured to nonmagnetic ears 0' on the core 0 with the line 1-2 joining its poles at an oblique angle to the vertical axis 3 4: of the core 0, instead of at right angles thereto, as is usually the case. The object of this arrangement is to allow the needle to stand in the position in which it appears in full lines in Fig. 7, and to swing to the dotted line position when the index reaches the outer end of the graduated scale H. This not only permits the minimum thickness for the frame D, with the longest range for the needle and index, but also admits of a better division of the scale, the division being much more uniform and regular. 7

To facilitate the standardizing of the permanent magnets, I provide a movable soft iron bridge preferably consisting of a flatbar I spanning the poles of the magnet and serving to weaken its strength. The bridge is preferably hinged at one end on a screw 1' tapped into one leg of the magnet. By swinging the bar one way or the other, as indicated by the dotted lines, a position will be found at which the strength of the magnet will equal a given standard. The bridge is then secured in this position by setting up the screw; The bar also acts as an armature or keeper for the magnet and tends to keep it permanent in strength.

Having thus described my invention, what I claim is 1. In a volt meter, a core containing a narrow transverse socket, in combination with a fiat frame removably inserted in said socket and containing bearings for the needle spin dle, substantially as described.

2. In a volt meter, the combination with a core having a transverse socket, of a flat frame removablyinserted therein, and a spinro c dle mounted in hearings in said frame and carrying a thin needle, and a damping device, substantially as described.

3. In a voltmeter, the combination with the field coils, of a permanent horse shoe magnet arranged with its poles on aline' oblique to the axis of the field coils, said coilslying between said poles, substantially as described.

4. In a volt meter, the combination with the bobbin 0 having a central flat socket at right angles to its axis, of a horse shoe magnet G having its poles on each side of said bobbin on a line oblique to the axis thereof, and a frame D received in said socket and carrying a needle e adapted to stand normally in the Q linebetween the poles of the magnet, substanspindle and inclosed in abox fittingit closely and provided with radial partitions, substantially as described.

6. In a voltmeter,a damping device for the I spindle, consisting of abox containing two opone leg thereof, and a soft iron bridge bar hinged-on said screw, and adapted to be clamped thereby when adj usted,substantially as described.

In testimony whereof I have hereunto set my hand in the presence of two witnesses.

EDWARD R. KNOWLES.

' Witnesses:

D. J. GLAZIER, F. S. CODY. 

